Structural composites and other reinforced molded articles are commonly made by resin transfer molding and structural resin injection molding. These molding processes have been made more efficient by preforming the reinforcement fibers into a reinforcement layer or mat, which is the approximate shape and size of the molded article, prior to inserting the reinforcements into the mold. To be acceptable for production at an industrial level, a fast preforming process is required. In the manufacture of preforms, a common practice is to supply a continuous length of reinforcement strand or fiber to a chopper, which chops the continuous fiber into many discrete length fibers, and deposits the discrete length fibers onto a collection surface. This process can be used to make preforms in an automated manner by mounting the reinforcement dispenser for movement over the collection surface, and programming the movement of the dispenser to apply the reinforcement fibers in a predetermined, desired pattern. The reinforcement dispenser can be robotized or automated, and such reinforcement fiber dispensers are known art for such uses as making preforms for large structural parts, as in the auto industry, for example.
Typically, the sprayed up or deposited fibers are dusted with a powdered binder, and compressed with a second perforated mold. Hot air and pressure sets the binder, producing a preform of reinforcement fibers which can be stored and shipped to the ultimate molding customer which applies resin to the preform and molds the resinated preform to make a reinforced product, typically using a resin injection process. The process of cutting continuous reinforcement fibers into discrete lengths of reinforcement fibers is useful in the manufacture of laminates as well as in the manufacture of preforms. Dispensers of reinforcement fibers for the manufacture of laminates can also be adapted to be moveable and programmable.
As the technical requirements for reinforcement products increases, new methods for dispensing and laying down reinforcement fibers are required. One requirement is that the reinforcement fibers be delivered at faster speeds than used previously. Another requirement is that the reinforcement fibers be laid down in varying degrees of thickness or density over the collection surface to achieve the desired reinforcement result. The advancement in the preform making technology enabling a moveable and programmable reinforcement fiber dispenser has led to requirements for very sophisticated fiber patterns and orientations. Preforms can be designed with specific amounts and orientations of reinforcement fibers to improve the strength of the molded product precisely at the weakest or most stressed location of the product to be molded. Because of this new sophistication, there often is a requirement that the fibers be laid onto the collecting surface in a very controlled manner.
Efforts to vary the delivery, particularly the width of the flow of chopped fibers dispensed by the fiber dispenser, have not been entirely successful, especially at the high speeds necessary for commercially successful operations. When typical strand chopper nozzles are operated at a faster speed, the resulting discrete reinforcement fibers cannot be successfully laid down in pattern that is as controlled as is desired.
It is clear that improvements in cutting continuous reinforcement fibers into discrete lengths and dispensing them in a controlled manner, enabling a more prescise distribution of fibers, would be desirable.